Current techniques for the preservation of fresh produce consist of temperature and/or pressure treatment or control, wax and similar coating techniques, synthetic polymer coating techniques, and polymer packaging.
Various coating compositions have been proposed, e.g., a petroleum solvent solution of a waxy film former and a fungicide (U.S. Pat. No. 4,006,259), a mixture of lard, tallow and lecithin applied in molten state (U.S. Pat. No. 4,207,347), hydrogenated jojoba oil (U.S. Pat. No. 4,356,197), a salt of carboxylic acid and an alkyl amine (U.S. Pat. No. 4,532,156), a 3% oil-in-water emulsion of hydrogenated vegetable oil, stearic acid and an anionic emulsifier (U.S. Pat. No. 4,649,057), the combination of a food acid, an edible reducing agent and a carbohydrate thickener followed by freezing (U.S. Pat. No. 4,751,091), a denatured proteinaceous solution of soybeans, wheat and corn (U.S. Pat. No. 5,128,159), simultaneously scrubbing and drenching with a liquid containing a fungicide (U.S. Pat. No. 5,148,738), a slurry consisting of by-products of the produce and certain sugars and acids (U.S. Pat. No. 5,364,648), a mixture of a polysaccharide polymer, a preservative, an acidulent and emulsifiers (U.S. Pat. No. 5,198,254), and a light-activated composition (U.S. Pat. No. 5,489,442).
Some Russian and Japanese publications have proposed the use of polyvinyl alcohol as a gas barrier coating for produce, but few if any of these suggestions have found their way into the commercial market.
Various forms of produce packaging are disclosed, by way of example, in U.S. Pat. Nos. 4,769,262; 5,030,510; 5,093,080; 5,160,768; 5,427,807; 5,547,693; and 5,575,418.
In the case of bananas, to which the present invention has particular application, the bananas are harvested in a green, unripened state, washed to remove field debris, and refrigerated for shipment via "reefer boats" (refrigerated vessels) to a point of distribution. At destination, the green bananas are transferred to cold storage warehouses where they remain until transferred to temperature controlled ripening rooms. In the ripening rooms, the bananas are exposed to ethylene gas to trigger the ripening process. Once triggered, the ripening process cannot be halted and the bananas must be delivered in real time to retail outlets for sale before the bananas become overripe, discolored and unsalable. Green tomatoes are treated in a similar fashion.
Coating the produce with a solvent solution of natural wax products will extend their storage life, but the solvent for the wax can be both expensive and environmentally hazardous. Consequently, wax coatings have not met with widespread acceptance.
A synthetic polymer coating for bananas, available under the brand name "SEMPERFRESH", is based on sucrose esters of fatty acids. The bananas are coated by dipping in a dilute suspension of the SEMPERFRESH product and allowed to dry, which results in a thin, invisible coating on the surface of the peel. In a study of the effect of SEMPERFRESH coatings on the preservation of bananas transported under refrigerated conditions and stored under non-refrigerated conditions, ripening was found to be delayed without adverse effect on flavor. However, the coating only allowed storage of bananas at ambient temperatures for about 10 days.
Enclosing bananas in polyethylene bags is also effective. The thickness and porosity of the packaging must be appropriate to the physiological reactions of the fruit. This results in the creation of a modified atmosphere that slows water loss and respiratory exchange, but also induces undesirable symptoms due to asphyxia. Here again, the use of polyethylene bags allows storage of bananas at ambient temperatures for only a few days.